Gloss · Words · Pernicious vs insidious
Pernicious vs insidious
Insidious is about how the harm arrives: slowly, unnoticed. Pernicious is about how bad it is.
The difference
Insidious describes the method. An insidious disease, an insidious habit, an insidious idea: they get in gradually and do their damage before anyone notices. The word is about stealth. Pernicious describes the effect. A pernicious influence is seriously harmful, and it may be perfectly obvious. The word is about damage, not concealment.
Pernicious
Doing harm slowly and quietly, so you notice it late.
Gossip had a pernicious effect on the office.
Pernicious, explained six ways
Insidious
Spreading harm slowly and quietly, so you do not notice.
The disease is insidious in its early stages.
Which one to use
If the danger is that nobody sees it coming, insidious. If the danger is simply how much harm it does, pernicious. A thing can be both.
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